Temperature sensing provides vital information about the condition, safety and state of health of items and individuals, for example, in the supply chain of perishables, foods, pharmaceuticals and other temperature sensitive goods, for medical observation and medical diagnostics as well as for homeland security.
The novel one point calibration integrated temperature sensor described herein is intended for integration into low cost wireless transceiver platforms such as, but not limited to, passive Radio Frequency Identification (RFID) transceiver chips, where very little additional power consumption is available for on-chip or off-chip sensors. The invention thereby facilitates the transformation of passive RFID tags into low cost platforms that can be used for a variety of different sensing applications.
In many state of the art consumer, commercial and medical microelectronic applications, where the minimization of power consumption is of primary concern, analog circuits can be designed, by those skilled in the art, to consume considerably less power than digital circuits that perform the same or similar function.
Several analog integrated temperature sensors have been proposed. Typically, these circuits are referred to as PTAT (proportional to absolute temperature) or CTAT (complimentary to absolute temperature) and are frequently utilized in band gap voltage references where their inherent nonlinear temperature dependence is undesirable because it requires more than a one point temperature calibration to map the sensor's nonlinear output response to an accurate temperature reading. This requires a look-up table that must reside in memory either on the wireless transceiver sensor chip itself or in the wireless transceiver sensor chip reader. Moreover, additional circuitry, surface area and power consumption are required to startup PTAT and CTAT circuits as well as to attempt to nullify second and higher order nonlinearities.